The present invention generally relates to papermaking belts useful in papermaking machines for making strong, soft, absorbent paper products. The invention is also concerned with a method of making such papermaking belts. More particularly, the invention relates to papermaking belts comprising a resinous framework and a reinforcing structure joined thereto.
Generally, a papermaking process includes several steps. Typically, an aqueous slurry of papermaking fibers is formed into an embryonic web on a foraminous member, such, for example, as a Fourdrinier wire. After the initial forming of the paper web on the Fourdrinier wire, or forming wires, the paper web is carried through a drying process or processes on another piece of papermaking clothing in the form of endless belt which is often different from the Fourdrinier wire or forming wires. This other clothing is commonly referred to as a drying fabric or belt. While the web is on the drying belt, the drying or dewatering process can involve vacuum dewatering, drying by blowing heated air through the web, a mechanical processing, or a combination thereof.
In through-air-drying processes developed and commercialized by the present assignee, the drying fabric may comprise a so-called deflection member having a microscopically monoplanar, continuous, and preferably patterned and non-random network surface which defines a plurality of discrete, isolated from one another deflection conduits. Alternatively, the deflection member may comprise a plurality of discrete protuberances isolated from one another by a substantially continuous deflection conduit, or be semi-continuous (i.e., comprising a combination of the continuous and discrete network). The embryonic web is associated with the deflection member. During the papermaking process, the papermaking fibers in the web are deflected into the deflection conduits and water is removed from the web through the deflection conduits. The web then is dried and foreshortened, if desired, by creping. Deflection of the fibers into the deflection conduits of the papermaking belt can be induced by, for example, the application of differential fluid pressure to the embryonic paper web. One preferred method of applying differential pressure is exposing the web to a fluid pressure differential through the drying fabric comprising the deflection member.
Through-air-dried paper webs may be made according to any commonly assigned and incorporated herein by reference U.S. Pat. No. 4,529,480 issued to Trokhan on Jul. 16, 1985; U.S. Pat. No. 4,637,859 issued to Trokhan on Jan. 20, 1987; U.S. Pat. No. 5,364,504, issued to Smurkoski et al. on Nov. 15, 1994; U.S. Pat. No. 5,259,664, issued to Trokhan et al. on Jun. 25, 1996; and U.S. Pat. No. 5,679,222, issued to Rasch et al. on Oct. 21, 1997.
Generally, a method of making the deflection member comprises applying a coating of liquid photosensitive resin to a surface of a foraminous element, controlling the thickness of the coating to a pre-selected value, exposing the coating of the liquid photosensitive resin to light in an activating wave-length through a mask, thereby preventing or reducing curing of selected portions of the photosensitive resin. Then the uncured portions of the photosensitive resin are typically washed away by showers. Several commonly assigned U.S. Patents which are incorporated herein by reference, disclose methods of making papermaking belts: U.S. Pat. No. 4,514,345, issued Apr. 30, 1985 to Johnson et al.; U.S. Pat. No. 4,528,239, issued Jul. 9, 1985 to Trokhan; U.S. Pat. No. 5,098,522, issued Mar. 24, 1992; U.S. Pat. No. 5,260,171, issued Nov. 9, 1993 to Smurkoski et al.; U.S. Pat. No. 5,275,700, issued Jan. 4, 1994 to Trokhan; U.S. Pat. No. 5,328,565, issued Jul. 12, 1994 to Rasch et al.; U.S. Pat. No. 5,334,289, issued Aug. 2, 1994 to Trokhan et al.; U.S. Pat. No. 5,431,786, issued Jul. 11, 1995 to Rasch et al.; U.S. Pat. No. 5,496,624, issued Mar. 5, 1996 to Stelljes, Jr. et al.; U.S. Pat. No. 5,500,277, issued Mar. 19, 1996 to Trokhan et al.; U.S. Pat. No. 5,514,523, issued May 7, 1996 to Trokhan et al.; U.S. Pat. No. 5,554,467, issued Sep. 10, 1996, to Trokhan et al.; U.S. Pat. No. 5,566,724, issued Oct. 22, 1996 to Trokhan et al.; U.S. Pat. No. 5,624,790, issued Apr. 29, 1997 to Trokhan et al.; U.S. Pat. No. 5,628,876 issued May 13, 1997 to Ayers et al.; U.S. Pat. No. 5,679,222 issued Oct. 21, 1997 to Rasch et al.; and U.S. Pat. No. 5,714,041 issued Feb. 3, 1998 to Ayers et al., the disclosures of which are incorporated herein by reference.
While curing of the photosensitive resin has proved to be an effective way of making the papermaking belt, a search for improved methods and products has continued. Now, it is believed that the deflection member may be made by at least several other methods which do not necessarily require the use of the curing radiation.
Accordingly, it is an object of the present invention to provide a novel process for making a papermaking belt by first, forming a desired pattern of a fluid resin in a molding member, and then transferring the resin from the molding member to the reinforcing structure and solidifying the patterned resin. Another object of the present invention is to provide a process that reduces the amount of the resin required to construct the papermaking belt comprising a reinforcing structure and a patterned resinous framework. Still another object of the present invention is to provide an apparatus comprising a molding member for forming a desirable pattern of the resin and subsequently transferring the patterned resin to the reinforcing structure of the belt being constructed.
These and other objects of the present invention will be more readily apparent when considered in reference to the following description, in conjunction with the accompanying drawings.
A papermaking belt that can be made by a process and an apparatus of the present invention comprises a reinforcing structure and a patterned resinous framework joined thereto. The reinforcing structure has a first side and an opposite second side. Preferably, but not necessarily, the reinforcing structure comprises a fluid-permeable element, such as, for example, a woven fabric or a screen having a plurality of open areas therethrough. The reinforcing structure may also comprise a felt. The resinous framework has a top side and a bottom side, the top and bottom sides corresponding to the first and second sides of the reinforcing structure, respectively. The resinous framework may have a substantially continuous pattern, a discrete pattern, or a combination thereof (i.e., a xe2x80x9csemi-continuous patternxe2x80x9d).
A process for making the belt comprises the following steps: providing a reinforcing structure having a first side, a second side opposite to the first side, and a thickness formed therebetween; providing a flowable resinous material; providing at least one molding member having a molding surface comprising a pre-selected pattern of molding pockets structured and designed to carry the flowable resinous material therein; continuously moving the molding surface at a transport velocity; depositing the flowable resinous material into the molding pockets of the molding surface; continuously transporting the reinforcing structure at the transport velocity such that at least a portion of the reinforcing structure is in a face-to-face relationship with at least a portion of the molding surface; transferring the flowable resinous material from the molding pockets of the molding surface onto the reinforcing structure; causing the flowable resinous material and the reinforcing structure to join together; and solidifying the resinous material thereby forming the resinous framework joined to the reinforcing structure. Preferably, the resinous material is transferred from the molding pockets onto the reinforcing structure in the predetermined pattern corresponding to the pattern of the molding pockets. Preferably, a step is provided of treating the molding surface with a release agent prior to depositing the resinous material onto/into the molding surface. When the reinforcing structure is in a face-to-face relationship with the molding surface, preferably the reinforcing structure contacts the flowable resinous material disposed in the molding pockets for a predetermined period of time sufficient to cause the flowable resinous material and the reinforcing surface to at least partially join together. The transferal of the resinous material from the molding surface onto the reinforcing structure may be assisted by pressing the molding surface and the reinforcing structure relative each other.
An apparatus for making the papermaking belt has a machine direction and comprises a molding member having a patterned molding surface comprising a plurality of molding pockets. The molding pockets are structured and designed to carry a flowable resinous material therein. In one embodiment, the molding member comprises a rotatable molding roll having a circumference and a longitudinal axis of rotation perpendicular to the machine direction. The circumference of the molding roll comprises the molding surface. In another embodiment, the molding member comprises an endless molding band adapted to continuously travel in the machine direction.
The apparatus further comprises a means for depositing the flowable resinous material into the molding pockets of the molding surface, a means for moving the reinforcing structure in the machine direction such that at least a portion of the reinforcing structure is in a face-to-face relationship with at least a portion of the molding surface, and a means for moving the molding member in the machine direction such that the flowable resinous material is transferred from the molding pockets onto the reinforcing structure, preferably in a pre-selected pattern. The apparatus preferably further comprises a means for solidifying the flowable resinous material such as to form the resinous framework joined to the reinforcing structure.
In one embodiment, the molding pockets of the molding surface form a substantially continuous pattern, in which instance the resinous material is transferred onto the reinforcing structure in a substantially continuous pattern. In another embodiment, the molding pockets of the molding roll form a pattern of discrete molding pockets, in which instance the resinous material is transferred onto the reinforcing structure in a pattern comprising discrete resinous protuberances. An embodiment is contemplated in which the molding pockets of the molding surface form a combination of the substantially continuous pattern and the discrete pattern, a so-called xe2x80x9csemi-continuousxe2x80x9d pattern.
The resinous material may, in some embodiments, extend outwardly from the first side of the reinforcing structure after the resinous material has been deposited onto the reinforcing structure. The molding pockets have a depth therein, which may differentiate throughout different parts of the molding surface. The present invention allows one to make the belt in which the resinous framework has differential thickness throughout the belt""s plane. At the same time, the present invention allows one to construct the belt in which the top side of the resinous framework and the first side of the reinforcing structure lie in substantially the same plane.
The flowable resinous material is preferably selected from the group consisting of epoxies, silicones, urethanes, polystyrenes, polyolefins, polysulfides, nylons, butadienes, photopolymers, and any combination thereof. In one preferred embodiment the fluid resinous material comprises a photosensitive resin. The fluid resinous material may comprise a thermo-sensitive resin, such as thermo-setting or thermoplastic material. Preferably, the fluid resinous material is provided in a liquid state. The fluid resinous material may be deposited onto/into the molding surface by first, contacting the molding surface with the flowable resinous material and second, removing excess of the flowable resinous material from the molding surface as the molding surface is moving.
The apparatus further may comprise a means for pressing the reinforcing structure and the molding surface relative to each other for a predetermined period of time, thereby facilitating the transferal of the resinous material from the molding surface to the reinforcing structure. In one embodiment, the apparatus comprises a backing roll juxtaposed with the molding surface to form a nip therebetween. In another embodiment, the apparatus comprises a backing sheet juxtaposed with the molding surface. The backing sheet is structured and designed to move in a face-to-face contacting relationship with at least a portion of the reinforcing structure. Preferably, the backing sheet is tensioned.
In one embodiment, the molding surface comprises a predetermined pattern of recesses. The recesses are structured and designed to receive the reinforcing structure therein. This embodiment provides the belt in which a substantial portion of the bottom side of the resinous framework is elevated above the second side of the reinforcing structure. That is, the belt has a distance formed between the second side of the reinforcing structure and the substantial portion of the bottom side of the resinous framework. During a papermaking process, this distance provides leakage between the belt and a dewatering papermaking equipment, thereby eliminating a sudden application of fluid pressure differential to a paper web disposed on the belt and mitigating a phenomenon known as xe2x80x9cpinholling.xe2x80x9d The distance between the second side of the reinforcing structure and the bottom side of the resinous framework may differentiate throughout the plane of the belt.
The apparatus may further comprise a means for solidifying the flowable resinous material, such as, for example a curing device comprising a source of UV radiation, for curing the resinous material comprising a photosensitive resin. Optionally, a step and a means may be provided of controlling a thickness of the resinous material joined to the reinforcing structure to at least one pre-selected value.